1. Field of Invention
This application relates generally to the surface mount of electronic components onto a printed circuit board by employing a reflow process, and more particularly to a system and method for extracting and collecting vaporized contaminants (e.g., flux) out of a reflow oven, and removing the collected contaminants without interrupting the surface mount production.
2. Discussion of Related Art
In the fabrication of printed circuit boards, electronic components are often surface mounted to a bare board by a process known as “reflow soldering.” In a typical reflow soldering process, a pattern of solder paste is deposited onto the circuit board, and the leads of one or more electronic component are inserted into the deposited solder paste. The circuit board is then passed through an oven where the solder paste is reflowed (i.e., heated to a melt or reflow temperature) in the heated zones and then cooled in a cooling zone to electrically and mechanically connect the leads of the electronic component to the circuit board. The term “circuit board,” as used herein, includes any type of substrate assembly of electronic components, including, for example, wafer substrates.
Solder paste typically includes not only solder, but also flux to promote solder wetting and to provide good solder joints. Other additives, such as solvents and activators, can also be included. After the solder paste is deposited on the circuit board, the circuit board is passed on a conveyor through a plurality of heating zones of a reflow soldering machine. As the solder paste melts, volatile organic compounds (referred to as “VOCs”) in the flux and other additives are vaporized and tend to condense in the reflow machine. In many of the reflow furnaces, soldering is performed in an inert atmosphere using primarily nitrogen to reduce oxidation on solder surfaces.
In certain reflow machines, the heating zones are separated into a number of different zones, including pre-heat zones, soak zones, and spike zones. In the pre-heat zones and the soak zones, the products are heated and the VOCs in the flux vaporize in the surrounding gas atmosphere. The spike zones are hotter than the pre-heat and soak zones, and it is in the spike zones that the solder melts. The spike zones are also the zones where higher temperature VOCs, such as rosin or resin, will vaporize. A reflow soldering machine may have many heating zones, and these heating zones may be varied depending on the products to be soldered. Different products require different heat profiles, and the reflow soldering machine should be flexible so that, in one example, a machine with ten heating zones may have one pre-heat zone followed by seven soak zones and two spike zones for one type of circuit board, and for a different type of board may have three pre-heat zones, six soak zones and one spike zone. One or more cooling zones follow the heating zones in which the solder solidifies on the solder areas (e.g., electronic pads typically fabricated from copper or a copper alloy) of the circuit board.
If VOCs pass from the heating zones into the cooling zones, those compounds have a tendency to condense in the cooling zones. This condensate may impair cooling functions and may present processing problems. The most common problem occurs with no-clean, enhanced, print performance solder pastes. These pastes utilize viscosity modifiers to achieve superior printing performance. Problems may arise when the viscosity modifying components condense in the cooling zones. By nature, these residues are a viscous liquid and can build up and drip onto the soldered product from the cooling zone surfaces, such as heat exchangers positioned within the cooling zones.
Known methods for removing these VOCs typically employ heat exchangers that cool a hot gas stream removed from a process chamber and thereby condense organic compounds in the gas stream on a surface of the heat exchanger. The condensate can then be removed with a condensate filter before the gas stream is returned to the process chamber. With such known methods, the condensate filter must be cleaned periodically, which requires the interruption of the reflow oven.